A stacked multi-chip module includes semiconductor devices such as two or more discrete transistors and a control integrated circuit, in a stacked configuration, on a lead frame unit. The lead frame unit is part of a lead frame array which has a plurality of multi-chip module sites. One or more clips make electrical connections between the semiconductor devices and pins of the lead frame. The clips are typically copper foil that has been stamped into the desired shape. The clips are separated from a clip tape and placed onto the multi-chip module sites. The clips are electrically coupled to the semiconductor devices by solder, which is reflowed during assembly of the multi-chip module. During solder reflow, single clips may rotate and/or tilt, leading to defects in the multi-chip module such as solder extending beyond the clips and causing a short circuit, and/or insufficient solder between the clip and the corresponding semiconductor device.
This problem has been addressed by using gang clips which have a clip for each multi-chip module site of the lead frame array. The clips in the gang clip are linked together by tie bars. Gang clips, usually produced by masking and etching operations, are more costly than clip tapes. Furthermore, gang clips commonly have several tie bars per clip, which are severed during singulation of the lead frame array, undesirably increasing wear on the saw blade used for singulation.
This problem has also been addressed by the invention described in U.S. Pat. Nos. 9,472,491 and 9,171,788. These patents describe a lead frame with adjacent lead frame units that are rotated 180 degrees with respect to each other, and a corresponding first and second clip sets that are likewise rotated 180 degrees with respect to each other. Lead frames with lead frame units that are rotated 180 degrees, being nonstandard, add cost and complexity to the multi-chip module assembly process. Moreover, die placed on the rotated lead frame units must be rotated during pick and place operations, further adding to cost and cycle time. Furthermore, it is not always feasible to have adjacent lead frame units that are rotated 180 degrees with respect to each other, due to placement of the clip contacts. The clip contact areas depicted in U.S. Pat. Nos. 9,472,491 and 9,171,788 consume more space than commonly used clip feet.